Antimetabolites such as 5-azacytidine and 5-fluorouracil are believed to exert antitumor effects, at least in part, through their incorporation into mRNA, and hence their interference with the ability of mRNA to code for proteins critical to the balanced growth of the cell. This hypothesis will be tested by quantitative and qualitative assessment of the capacity of polysomal poly (A) RNA from regenerating liver or Ehrlich ascites cells to code for proteins in heterologous cell-free translation systems derived from wheat germ and reticulocytes. These studies will include analyses of the drug-modified poly (A) RNA by agarose gel electrophoresis, and analysis of translation products both quantitatively and qualitatively by polyacrylamide slab gel electrophoresis and autoradiography. Assessment of initiation complexes between ribosome and poly (A) RNA will be carried out with sucrose gradient centrifugation using (3 H) poly (A) RNA or (3H) methionyl-tRNA.